1 Power-off method
Utilizing the characteristics of electromagnetic noise that varies with the strength of the magnetic field, the size of the load current, and the level of conversion, the power supply is suddenly cut off after a period of quiet listening to the motor running at no load, and the noise will disappear immediately as the power supply is cut off. This is electromagnetic noise. After a power failure, the noise generated by the inertia of the motor continuing to run is mechanical noise. Repeat several times to be sure.
2 Change the voltage method
When the power supply voltage drops rapidly to a certain limit (the speed does not change significantly), if electromagnetic noise is the main part of the motor noise, it will vary greatly with the voltage, and the noise for other reasons is basically the same.
3 Current test method
If the stator winding of the miniature geared motor is asymmetrical or internal phase failure or short-circuit between turns, the current will be unbalanced; if the rotor cage is broken or the rotor of the wound motor is asymmetrical, the stator current will fluctuate to identify electromagnetic noise.
4 Drag method
Use a low-noise motor to drive the motor under test to rotate, and lift and lower the carbon brush several times to identify the effect of carbon brush noise.
5 disassembly method
The characteristics of stable aerodynamic noise can be identified by the changes in noise before and after removing the fan of the miniature geared motor or the external blower (large and medium-sized motors). In addition, by replacing fans with different outer diameters and types, distinguishing the difference in noise at different speeds, the fan noise can also be identified.